C#: Add more invalid-string-formatting testcases.

Author: michaelnebel

csharp/ql/test/query-tests/API Abuse/FormatInvalid/FormatInvalid.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Globalization;
 using System.Text;
 
 class FormatInvalid
@@ -134,5 +135,27 @@ void FormatMethodTests()
         ts.TraceInformation("{0}"); // GOOD
     }
 
+    void CompositeFormatMethods()
+    {
+        var format = CompositeFormat.Parse("}"); // $ Alert
+
+        // GOOD: Format is invalid and this flagged during parsing.
+        String.Format<string>(null, format, "");
+        String.Format<string, string>(null, format, "", "");
+        String.Format<string, string, string>(null, format, "", "", "");
+
+        sb.AppendFormat(null, format, "");
+        sb.AppendFormat<string>(null, format, "");
+        sb.AppendFormat<string, string>(null, format, "", "");
+        sb.AppendFormat<string, string, string>(null, format, "", "", "");
+
+
+        var span = new Span<char>();
+        span.TryWrite(null, format, out _);
+        span.TryWrite<object>(null, format, out _, new object());
+        span.TryWrite<object, object>(null, format, out _, new object(), new object());
+        span.TryWrite<object, object, object>(null, format, out _, "", "", "");
+    }
+
     System.IO.StringWriter sw;
 }